Valve sends an explanation for why Half-Life 2 is not being activated at this
time in spite of the couple reports of it being available at retail already:

Half-Life 2 For Sale?

If you have purchased a copy of Half-Life 2, we are sorry you are still waiting
to play. This is not Valve's choice. Vivendi is insisting that the game has not
yet been released, and has threatened that Valve would be in violation of its
contract if we activate the Half-Life 2 Steam authentication servers at this
time.

Thanks for your patience and we will update you when we have more news to
share.

If the Steam servers hold up I think this could be one of the smoothest game releases ever. Think about it, with a lot of games we all end up calling or driving around town hoping to find a store that has received their copies. Either that or you're waiting by the door hoping for the big brown truck to drive up.

This Tuesday we can (in theory) either fire up our pre-installed game or be confident that our favorite stores will have a copy in stock. This isn't the norm for most major game releases. Of course the pre-order people are still at the mercy of the shipping departments.

As you all can probably tell, I'm not ready to put all my trust into Steam yet. I'll believe it when I see it, but I guess I've put enough faith into it to be using it now.

-------------------------------------------------------"Give me a Sandwich and a Douchebag and there is nothing I cannot do." ~ Lord Salisbury